The purpose of this study is to identify predictors of mental retardation in a population of 37,000 children followed from the prenatal period to age 7. The incidence of mild retardation (1% in whites and 5% in blacks) and to a lesser degree, of severe retardation (0.5%) was inversely related to socioeconomic status. Among the severely retarded, 25% of whites and 50% of blacks had no major genetic or neurological abnormality. Perinatal risk factors for the severly retarded group as a whole include Down's syndrome, major CNS malformations, neonatal seizures and clinical signs of perinatal hypoxia. for the subgroup of severely retarded with unknown etiology, perinatal risk factors include non-CNS malformations, peripheral nerve abnormalities, signs of hypoxia, and maternal urinary tract infection during pregnancy. Results of multivariate analyses of drugs taken during pregnancy showed that barbiturates non-barbituate anticonvulsants, and phenothiazines were associated with severe mental retardation in the offspring in both ethnic groups. A report on selected risk factors for deficits in early cognitive development is in press. This study is completed and a monograph is in preparation.